The present invention relates to a power supply control device controlling power feeding to a load to be connected thereto using an FET, and to a power supply control circuit effectively using different types of FETs in accordance with an operation state of the load to appropriately adjust power consumption and realize power supply control with high efficiency, and relates to a power supply control device controlling the power feeding using the control circuit.
Recently, each device (load) may be configured to switch to a state with low power consumption such as a power-saving mode or a sleep mode and to operate therein, because energy saving is desired in various fields.
Particularly in the field of vehicles, the volume of devices mounted on a vehicle (load) tends to increase, while enhancement in fuel consumption is desired. Among such vehicle-mounted devices, some devices are desired to constantly supply power regardless whether the engine is stopped or running because of enhanced functions of a vehicle as a whole. Since, however, power consumption needs to be reduced for lower fuel consumption, power feeding to each vehicle-mounted device needs to be precisely controlled. For example, power feeding to a vehicle-mounted device which is not being used is stopped in order to reduce dark current. Thus, a configuration including a device for controlling power supply between a power supply and each vehicle-mounted device is realized.
An FET (Field Effect Transistor) is utilized as a switching element in power feeding control with respect to each device, particularly in high-side control for performing control on the positive polarity side of a power supply. In the high-side control, a mechanism for protecting each element is required in order to satisfy high reliability. Especially for the high-side control in the field of vehicles, power supply voltage may temporarily be unstable and may be used under high temperature. It is essential to protect devices because a failure in power supply to a vehicle-mounted device causes a danger. Moreover, in the field of vehicles, power supply voltage may temporarily be low at cranking due to a starter consuming a large amount of current. It is thus desired that control can be performed such that power feeding to each device will not be unstable at low voltage. Furthermore, in order to minimize voltage drop from power supply voltage, a device in which power supply control is realized is desired to have low on-resistance. In addition, power consumption is desired to be reduced also in power control when the entire vehicle-mounted system as a whole can be transferred to a low power consumption state (sleep state), such as when the vehicle is stopped.
Conventionally, there are some cases where a discrete FET is employed as the FET used in the high-side control. The configuration with the discrete FET, however, does not have a sufficient protective function. For example, a configuration has proposed in which a P-channel MOSFET (Metal Oxide Semiconductor FET) is further provided with an N-channel MOSFET as a protection element. Other than the protective function disclosed in the example, a device of IPS (Intelligent Power Switch) containing an FET and a protection element may be utilized. This enables the FET to be protected from overheat, overcurrent or overvoltage.